1. Field of the Invention
The present invention provides apparatus capable of removing both bark and limbs from trees or tree parts. However, since the apparatus may be used only for removing bark, or only for removing limbs, references to "debarking/delimbing" apparatus and the like will be understood to include apparatus suitable only for debarking or only for delimbing.
While apparatus of this invention may have many different applications, a particular utility is in debarking and delimbing small trees, especially softwood trees, from about 1 inches to about 12 inches diameter, of the type used to produce pulp for paper making. For the production of good quality paper, it is required that about 99% of the bark be removed. However, this invention can also be used to debark trees of up to 24 inches diameter, e.g. for the production of lumber.
2. Prior Art
Various rather complex and expensive debarkers have been designed and made for removing bark from trees in pulp mills. Simpler mobile debarkers have also been used in the forest. The trend in recent years has been to conduct debarking and delimbing in the forest, so that the bio-degradable waste products can immediately be returned to the forest floor.
One known kind of debarker is the so-called ring debarker, in which a ring, rotatable on its own axis, carries a series of arms which are pivotally mounted inside the ring and carry debarking tools which remove the bark from a tree fed through the ring. This has the drawback of being complex and expensive.
Another kind of debarker, and one which is mobile enough to be used in the forest, is the so-called flail debarker. This has one or two rotatable spools each with a series of chains which extend outwards from the spool when the spool is rotated at high speed. While these are commonly used, they have drawbacks. Firstly, they do not reliably remove all or almost all the bark. Secondly, breakage of the chains is common. Chain breakage not only adds to maintenance cost, but means that precautions have to be taken to prevent pieces of broken chain from entering processing equipment which receives the debarked wood. Also, metal fragments may make the waste products of the process unsuitable as fuel.
The present invention provides a spool device which is capable of removing bark from most of one side of a tree part, but which does not use loose members such as chains which are subject to breakage. Debarking apparatus using two of the spool devices of this invention is capable of removing most of the bark of tree parts fed between the spools, for example about 99% of the bark. The term "tree part" includes tree trunks and tree branches of more than 1 inch diameter.
Spool devices having movable debarking elements, intended as an improvement over chain flails, are described in prior U.S. Pat. No. 5,094,281, issued Mar. 10, 1992, and Canadian Patent Application No. 2,060,096, published Jul. 26, 1992, of which I am co-inventor.
Spool devices in the form of rollers having fixed debarking elements are known from the following patents:
U.S. Pat. No. 2,917,090, issued Dec. 15, 1959 to Streed; PA1 U.S. Pat. No. 3,088,504, issued May 7, 1963 to Stihl et al.; PA1 U.S. Pat. No. 4,875,511, issued Oct. 24, 1989 to Wingate-Hill et al.; PA1 U.S. Pat. No. 5,111,860, issued May 12, 1992 to Wingate-Hill et al.; PA1 U.S. Pat. No. 5,247,977, issued Sep. 28, 1993 to Munsey et al.; and PA1 Canadian Patent No. 729,954, issued Mar. 15, 1996 to Letts.
To Applicant's knowledge, none of these devices is in widespread use. A perceived drawback of these designs is that each spool or roller contacts only much less than 180.degree. of the circumference of a log, even with diameters of log for which they are designed, and the efficiency of the bark removal will usually fall significantly as the size of the log is reduced. Adequate debarking with such apparatus seems to require at least three rollers, and usually more, and is therefore complex and expensive. Accordingly, these devices do not offer an acceptable alternative to chain flail debarkers in which each spool can debark almost 180.degree. of the circumference of logs having a wide variety of sizes.
Thus, the Streed patent has three rollers or spools of different configurations which all act on one side of a log, but all these rollers would not contact more than about 140.degree. of the one side.
The Stihl et al. patent shows double cone rollers capable of contacting only a minor part of the circumference of a tree trunk, probably much less than 90.degree..
The Wingate-Hill '511 patent shows apparatus having three or more pairs of concave rollers, each of which seems to be capable of contacting about 100.degree. or 110.degree. of the circumference of logs which fit the concavity of the rollers; for smaller logs the contact surface would be much less. The '860 patent suggests that three of its double-cone rollers oriented at 120.degree. to each other may be sufficient for debarking logs; however debarking seems to rely on a substantial pressure being applied to the logs; since the double-cone rollers have a shallow angle each itself could hardly contact more than about one-quarter of a log circumference.
The Munsey et al. patent suggests the use of four concave rollers, each debarking somewhat more than one quadrant of a log. Here a complex mounting arrangement is provided for the rollers so that when used on logs of small diameter the axes of the rollers are twisted relative to each other to allow them to nest without interference. This suggests that the process relies on pressure, as in the Wingate-Hill patents, since otherwise the rollers could be spaced along the logs. In systems which rely on pressure, the need for rollers to be overlying or close to each other along the logs limits the maximum diameter of the rollers, and thus the amount that the sides of a roller can overlap and debark the sides of a log.
Another perceived drawback of these systems, particularly those of Wingate-Hill, is that processes which rely on pressure for removing bark are believed to only be suitable for certain types of wood, harvested at a time when they have adequate sap. Such processes are believed unsuited to North American softwoods which are frequently harvested in the winter months.
Canadian Patent No. 729,954 describes a spool device intended to replace chain flails. This has a parallel sided roller which would only contact a small proportion of one side of a log.
Relevant prior art also includes spool devices having flexible debarking elements, such as U.S. Pat. Nos. 2,769,468, issued Nov. 6, 1956 to Swanson, and 4,368,764, issued Jan. 18, 1983, to Peterson et al. The debarking elements used in these prior patents are flexible throughout their length, and rely largely on centrifugal forces to press them against logs being debarked. Although these may be effective in removing bark, the rotational speed needed to gain enough energy to delimb would probably cause excessive wear on the flexible elements.